For years, TV makers competed over price and screen size. Now they’re beating each other up over who is the most green.

The environmental friendliness of TVs is the new battleground for set manufacturers, at least from my interviews at Ceatec, a technology trade show taking place in the Tokyo suburb this week. Sony (NYSE:SNE), for instance, has a 42-inch LCD TV from 2005 on display that consumes 131 watts while showing programs. Next to it is a 2008 set of the same size consuming 57 watts to show the same program.

Sharp (OTCPK:SHCAY) also has two experimental TVs that run on solar power. One, a prototype 26-inch LCD TV, consumes only 40 watts of power - less power than a conventional light bulb requires. It functions on two solar small panels. Sharp is also showing off a 52-inch LCD TV that runs on a larger panel. It consumes only 220 kilowatt hours of solar power in an average year. (See photo below of the 26 inch).

Sharp has come out with an application for its new slim LCD TVs that display family pictures or paintings from the Old Masters while in sleep mode. Running this screensaver-like device only consumes 60 watts. (See photo below).

Meanwhile, Panasonic says it will reduce the power consumption in its plasma TVs by two-thirds by 2010 or 2011, said Toshihiro Sakamoto, president of Panasonic’s AVC Networks group in a meeting. The power consumption reduction will come in two ways. First, Panasonic will reduce the number of components in a plasma TV. Plasmas, which create images through chemical excitation, need more components than LCD TVs.

Second, Panasonic will try to direct more of the light coming from the light source to the screen itself. Doubling the luminance halves the electricity required to paint images on the screen, he said. Tripling it cranks down power to one-third.

“If the luminance effect is enhanced, we can dramatically reduce power,” he said.

Power consumption isn’t the only trick. Many TV makers continue to slim down their sets. Panasonic showed off a demo plasma that is under 27-millimeters thick, while Hitachi (HIT) and Sharp have already released (expensive) LCD TVs that are in the same range. Sony has an organic light-emitting diode TV that is far thinner, but smaller.

Smaller TVs require fewer materials, which cuts down on petroleum in the manufacturing process. And they’re lighter, making transportation easier, said Etsuhiko Shoyama, chairman of the board at Hitachi during a keynote presentation at the conference.

Hitachi earlier this year released thin LCD TVs in Japan that act as a convection oven, which dissipates heat better than fans or other devices. That allows the TV to be made thinner.